The embodiments described herein relate to the selective catalytic combustion of butanol to make olefins in good yield.
Butanols are a desirable hydrocarbon source for energy and chemical industries mainly because they are easily available through fermentation of non-food biomass and wastewater. Dehydration of butanol isomers (including 1-butanol, 2-butanol and isobutanol) produce butenes (including 1-butene, cis-2-butene, trans-2-butene and isobutene) which are highly valuable starting materials for chemical industries to make synthetic fuels, lubricants and other high value chemicals. For examples, 1-butene is used in the creation of high density polyethylene as well as linear low density polyethylene. 2-butene is an extremely valuable starting material for lubricants as well as agricultural chemicals. In olefin metathesis, 2-butene reacts with ethylene to form propylene. Isobutene is the starting material for butyl rubber, methyl tert-butyl ether (MTBE), and isooctane. In addition, synthetic petroleum kerosene (SPK) can be synthesized by oligomerization of 4-carbon olefins. Unlike dehydration of butanol in the prior art, this invention is an oxidative process (i.e., combustion). The combustion of 1-butanol is extremely exothermic and occurs via Equation 1 shown below. This heat production enables the reaction to perform auto-thermally. As a result, the catalytic reaction is activated to reach an authermal reaction temperature of 330° C. to 600° C. when the reactant stream (butanol vapor and oxygen) is preheated at approximately 200° C. In contrast, traditional dehydration process requires external heating to maintain catalyst temperature at about 300° C. to 500° C.CH3CH2CH2CH2OH+6O2→4CO2+5H2O ΔH=−2713 kJ/mol  (1)
In a combustion process, the equivalence ratio (φ) of a system, defined herein as the ratio of the fuel-to-air/oxidizer ratio to the stoichiometric fuel-to-air/oxidizer ratio, plays an important role in fuel conversion. Mathematically, the equivalence ratio is represented as:
                                                        ϕ              =                            ⁢                                                fuel                  ⁢                                      -                                    ⁢                  to                  ⁢                                      -                                    ⁢                  oxidizer                  ⁢                                                                          ⁢                  ratio                                                                      (                                          fuel                      ⁢                                              -                                            ⁢                      to                      ⁢                                              -                                            ⁢                      oxidizer                      ⁢                                                                                          ⁢                      ratio                                        )                                    st                                                                                                        =                            ⁢                                                                    m                    fuel                                    /                                      m                    ox                                                                                        (                                                                  m                        fuel                                            /                                              m                        ox                                                              )                                    st                                                                                                        =                            ⁢                                                                    n                    fuel                                    /                                      n                    ox                                                                                        (                                                                  n                        fuel                                            /                                              n                        ox                                                              )                                    st                                                                                        (        2        )            
where, m represents the mass, n represents number of moles, and suffix st stands for stoichiometric conditions.
The φ-value can be controlled by adjusting the amounts of fuel and/or oxygen that are reacted. Having a φ-value of unity (1) signifies a stoichiometric feed of fuel and air, as shown in the above equations. With reactions having high φ-values (i.e., values ranging from 0.75 to 3), the reaction is considered “fuel rich” and incomplete combustion occurs because not enough oxygen exists to combust the fuel. However, reactions having low φ-values (i.e., values ranging from 0 to 0.75) indicate reactions having a “fuel lean” environment with plenty of oxygen to oxidize the fuel into its combustion products: carbon dioxide and water.
The production of olefins from hydrocarbons is well known in the prior art. In particular, Patent Application Publication US2002/0087042 to Schmidt et al. teaches a process whereby ethane auto-thermally decomposes to form ethene. See also U.S. Pat. No. 6,566,573. However, this process only converts alkanes to mainly two and three carbon olefins, which are not as desirable as four carbon olefins to oligomerize into gasolines, jet fuels, diesel fuels or lubricants.
Patent Application Publications US 2008/0131948 and US 2008/0234523, both to Manzer et al., teach processes for converting dry and aqueous 2-butanol directly to isooctenes. However, these processes were carried out as batch processes, which are not favorable as a continuous flow reactor. Additionally, the butanol conversions were as high as 75%, but their selectivity into the desired iso-octenes was generally very low, which would create only a small product yield (yield=conversion×selectivity).
Patent Application Publications US 2008/0132730 and US 2008/0132732, both to Manzer et al., teach a process for producing butenes from dry and aqueous 2-butanol. In particular, US 2008/0132732 discusses achieving 100% conversion and 100% selectivity of a 70 wt % mixture of butanol. However, the reactions were carried out in a pressurized batch reactor (2 mL vials), making continual production impossible. Additionally, in US 2008/0132730, the selectivity and conversion of dry butanol was not as high, achieving only 75% conversion, and 100% selectivity. Both of these approaches used sulfuric acid (liquid) as the catalyst, which must then be separated from the liquid reactants, consequently adding another step. This implies frequent replacement of the catalyst, which would be expensive. These processes were also carried out in a pressurized batch reactor.